At present, in the recovery procedure of the branch clock of the synchronous digital hierarchy (SDH) optical terminal, or in the application of the end-to-end pseudowire emulation, it needs to recover the clock of E1 or T1, and the conventional method is: performing the frequency division operation on the high-speed clock to obtain the low-speed clock, however, in the procedure of the practical application, the high-speed clock cannot always be the integral multiple of the low-speed clock, so it needs to finely adjust the rate of the low-speed clock constantly. Since the low-speed clock is obtained from the frequency division of the high-speed clock, the difference is possible at least one high-speed clock period between the adjacent periods of the low-speed clock; that is to say, the jitter between the adjacent periods of the low-speed clock is at least one high-speed clock period. But the jitter of the low-speed clock is not what we need, that is, the smaller the jitter is, the better it is.
In the related art, the method for reducing the jitter is as follows: 1), improving the frequency of the high-speed clock, then the improvement of the frequency of the high-speed clock reducing the high-speed clock period correspondingly, therefore reducing the jitter of the low-speed clock correspondingly; 2), adding one analog phase lock loop behind the low-speed clock obtained by recovery, which can be used for eliminating the jitter.
Although the two above-mentioned methods achieve the objective of reducing the jitter, there are their own defects: in the method 1), due to the limitation of the current device function, it is impossible to infinitely add the frequency of the high-speed clock, that is to say, it is difficult to greatly increase the frequency of the high-speed clock, and improving the frequency of the high-speed clock will increase the power consumption greatly, and also increase the cost of the device; in the method 2), the analog phase lock loop is added behind the low-speed clock obtained by recovery, which increases the cost of device as well.